1. Field of the Invention
The invention relates to the manufacturing field of packaging machines, where a vertical packaging machine includes two opposite forming tubes.
2. Brief Description of the Background of the Invention Including Prior Art
Packaging machines with only one forming tube made up of one vertical packaging group set on the frontal face of a supporting structure are well known in the art. Said structure is equipped with a horizontal station that performs the transversal sealing of the packets or packages through a thermosealing pincer. In these packaging machines, the film comes from a roll, wraps itself up in the forming tube, and is welded longitudinally. This continuous tube of flexible material is pushed down by adherent belts and is filled upwards with the conditioning products to obtain finished packets by using a thermosealing pincer.
The possibility of disposing two vertical packaging machines side by side is also known in the art.
The French Patent document 2,250,676, the German Patent document DE 2,703,455, and the U.S. Pat. No. 4,081,943 teach packaging machines of a type which could represent prior art in the context of this application.
The British Patent document 1,065,144 discloses a vertical packaging machine with two opposite forming tubes 4,4, said packaging machine being made up of two different and separate vertical packaging groups, which are set on the opposite sides of a central structure 12, 22 that is equipped with a horizontal bilateral station 20 that carries out the transversal sealings of both resulting packets or packages, which are produced in a single transverse sealing step.
The configurations of the French Patent document 2,250,676, the German Patent document DE 2,703,455, the U.S. Pat. No. 4,081,943, and the British Patent document 1,065 144, respectively, are made up of two different vertical forming groups disposed side by side on the same wall of the supporting structure.
Each forming group according to this art is served by its own sealing transversal station.
In particular, the British Patent document 1,065,144 shows only one clamp which is elongated to hug both forming tubes. Said elongated clamp is set for two motions, the first motion being a vertical motion to go up and down and the second motion being a horizontal motion to open and to close. The clamp closes at the top dead center and then pulls with it the packaging materials in the downward motion. When the clamp reaches the dead bottom center, the clamp opens and goes up to reach the top dead center again. The kinematic motions and the structural choices described and illustrated in the above-cited references imply a cumbersome and uneconomical configuration with an unsatisfactory performance.
The structure shown in the British Patent document 1,065,144 presents only one frontal wall equipped with a pair of forming groups. Said groups are of necessity set side by side. The operational packaging cycle taught in the British Patent document 1,065,144 is by necessity only one, having only one elongated clamp 20 to work on both tubes of packaging material at the same time. Since only one packaging cycle is provided, the time of the upward motion is useless idle time. The open-shut motion of the elongated clamp 20 of the British Patent document 1,065,144 is performed by the rotation of the shaft 12. But this rotation of the shaft 12 is necessarily alternating. This alternating rotation is obtained with a chain pulled by the cam 82.